How do monopolies form?

Context: In the science fiction story I'm writing (set in 2050 San Francisco), there's a tech company that created a device similar to a smartwatch. This company is the backdrop for a lot of the worldbuildimg for this story. The device can be used to open portals into pocket dimensions.

Some of these pocket dimensions ended up with a ridiculous amount of energy inside them. They then harvested that energy, and I calculated that it has the potential to power the state of California for about eight years.

I'm thinking of expanding this idea. The energy is formed by matter that is sometimes destroyed by the pocket dimensions. Or rather, the pocket dimension collapses and, if there's stuff inside, it E = mc²'s it into pure energy.

So if residents had plastic waste they wanted to get rid of, that waste could be shoveled into the system owned by the company, and in return, more energy can be produced.

Could this easily become a monopoly, or are there other complications to consider? The company is leaps and bounds ahead of other companies in terms of technology, but I imagine some regulation or other complications might balance things out as well?